Fibers formed of synthetic polymers have long been recognized as useful in the production of textile articles. Such fibers can be used in diverse applications such as apparel, disposable personal care products, filtration media, and carpet.
It can be desirable to incorporate fine or ultrafine denier fibers into a textile structure, such as filtration media. Fine denier fibers may be used to produce fabrics having smaller pore sizes, thus allowing smaller particulates to be filtered from a fluid stream. In addition, fine denier fibers can provide a greater surface area per unit weight of fiber, which can be beneficial in filtration applications. Fine denier fibers can also impart soft feel and touch to fabrics.
It is, however, difficult to produce fine denier fibers, in particular fibers of 2 denier or less, using conventional melt extrusion processes. Meltblowing technology is one avenue by which to produce fabric from fine denier filaments. However, meltblown webs typically do not have good physical strength, primarily because less orientation is imparted to the polymer during processing and lower molecular weight resins are employed.
Multicomponent or composite fibers having two or more polymeric components may be split into fine fibers comprised of the respective components. The single composite filament thus becomes a bundle of individual component microfilaments. Typically multicomponent fibers are divided or split by mechanically working the fibers. Methods commonly employed to work fibers include drawing on godet rolls, beating or carding. Fabric formation processes such as needle punching or hydroentangling may supply sufficient energy to a multicomponent fiber to effect separation.
In addition, fine denier fibers can be prepared using a multicomponent fiber comprised of a desired polymer and a soluble polymer. The soluble polymer is then dissolved out of the composite fiber, leaving microfilaments of the other remaining insoluble polymer. The use of dissolvable matrixes, however, to produce fine denier filaments is problematic. Manufacturing yields are inherently low because a significant portion of the multiconstituent fiber must be destroyed to produce the microfilaments. The wastewater or spent hydrocarbon solvent generated by such processes poses an environmental issue. In addition, the time required to dissolve the matrix component out of the composite fiber further exacerbates manufacturing inefficiencies.
In addition to fine denier fibers, it can also be desirable to incorporate elastomeric fibers into textile structures to impart stretch and recovery properties. Elastomeric fibers or filaments are typically incorporated into fabrics to allow the fabrics to conform to irregular shapes and to allow more freedom of body movement than fabrics with more limited extensibility.
Elastomers used to fabricate elastic fabrics, however, often have an undesirable rubbery feel. Thus, when these materials are used in fabrics, the hand and texture of the fabric can be perceived by the user as sticky or rubbery and therefore undesirable. Non-elastomeric fibers can be commingled with elastomeric fibers and/or coated with an elastomeric solution to improve the feel of articles formed using elastic fibers. However, this requires additional processing steps, which can add manufacturing and materials costs.
Further, it can be difficult to process elastomeric materials to make elastic fibers or filaments. For example, many elastomeric yarns are formed of solvent spun elastomeric materials (Spandex). Elastomeric yarns can be produced by thermally extruding elastomeric filaments. However, one problem with this approach is breakage or elastic failure during extrusion and drawing. Due to the stretch characteristics of elastomeric polymers, the filaments tend to snap and break while being attenuated. If a filament breaks during production, the ends of the broken filament can either clog the flow of filaments or enmesh the other filaments, resulting in a mat of tangled filaments.
Elastic webs having fine denier elastomeric fibers can be produced using meltblowing technology. However, as noted above, meltblown webs typically do not have good physical strength. In addition, meltblown elastomeric webs generally have less aesthetic appeal.